Lamp and reflector assembly

ABSTRACT

A high-intensity arc lamp having anode and cathode stems extending in opposite directions from the bulb, is positioned in a reflector. The anode stem extends within a tapered hollow collar at the rear of the reflector, and the lamp is attached to the reflector by means of cement at the remote ends of the anode stem and hollow collar, whereby the hollow collar provides a heat-confining space around the anode stem for controlling the temperature and reducing the likelihood of thermal-stress cracking of the anode stem. A specially shaped connector within the reflector provides electrical connection to the cathode lead.

United States Patent Slomski Oct. 24, 1972 [54] LAMP AND REFLECTORASSEMBLY [72] lnventor: Stanley L. Slomski, Lyndhurst, Ohio [73]Assignee: General Electric Company [22] Filed: April 29, 1971 211 App].No.: 138,474

[52] US. Cl ..240/41.35 R, 240/11.4, 240/47 [51] Int. Cl ..F2lv 7/00[58] Field ofSearch.....240/l1.4 R, 11.2 R, 47, 41 A,

[56] References Cited UNITED STATES PATENTS 3,379,868 4/1968 Taillon..240/41.35 R

FOREIGN PATENTS OR APPLICATIONS 644,341 9/1962 Italy .[240/1 1.2 R 6,801,1 l7 8/ 1968 Netherlands ..240/1 1.2 R

Primary Examiner-Samuel S. Matthews Assistant Examiner-Richard L. MosesAttorney-Norman C. Fulmer, Henry P. Truesdell, Frank L. Neuhauser, OscarB. Waddell and Joseph B. Forman [57] ABSTRACT A high-intensity arc lamphaving anode and cathode stems extending in opposite directions from thebulb, is positioned in a reflector. The anode stem extends within atapered hollow collar at the rear of the reflector, and the lamp isattached to the reflector by means of cement at the remote ends of theanode stem and hollow collar, whereby the hollow collar provides aheat-confining space around the anode stem for controlling thetemperature and reducing the likelihood of thermal-stress cracking ofthe anode stem. A specially shaped connector within the reflectorprovides electrical connection to the cathode lead.

10 Claims, 2 Drawing Figures PATENTEDOcI 24 I972 Invenfiror: S tanLeg1.. SLomski His A ti'crneg LAMP AND REFLECTOR ASSEMBLY CROSS-REFERENCETO RELATED APPLICATION Patent application, Ser. No. 876,708, filed Nov.14, 1969, of Charles J. Miller, entitled Lamp and Housing Assembly nowU.S. Pat. No. 3,636,341, issued Jan. 18, 1972 and assigned to the sameassignee as the present invention (in Patent Office Group 285 BACKGROUNDOF THE INVENTION The invention is in the field of high-intensity lampand reflector assemblies, such as are particularly useful forphotographic projection purposes, e.g., movie projectors and slideprojectors. Such an assembly of a lamp and reflector is disclosed inU.S. Pat. No. 3,379,868 of John K. Taillon, issued Apr. 23, 1968 andassigned to the same assignee as the present invention. Thehigh-intensity arc lamp, which operates at a high temperature, comprisesa quartz envelope having a bulb-like arc chamber and, for d-c operation,an anode stem and a cathode stem extending in opposite directionstherefrom. The anode and cathode stems are elongated, and hermeticlead-in seals are made near the outer ends thereof, preferably bysealing the stems to thin metal foil sections welded intermediate thelamp electrodes and the inleads. In the aforesaid Taillon patent, thearc lamp is mounted perpendicular to the axis of the optical surface ofrevolution of the reflector, the end regions of the lamp being cementedin openings provided in the reflector.

Arc lamps of the aforesaid type have a tendency to develop cracks intheir envelopes at the vicinity of the stem seals, due to thermal stresscaused by high operating temperature and high thermal gradient along thestems. Such cracks are likely to permit air to enter, and fill gas toleave, the envelope thus destroying usefulness of the lamp. Indirectcurrent operation the anode electrode operates at highertemperature than the cathode electrode, and hence the anode stem seal isparticularly prone to cracking due to thermal stress. One technique forreducing the seal temperature is to increase the length of the stems ofthe lamp. For a d-c lamp, in which the anode operates hotter than thecathode, the anode stem may be made longer than the cathode stem, asshown in the aforesaid Taillon patent, to provide a more gradual thermalgradient. However, it is costly to lengthen the stems, and it isunfeasible to extend them unduly, particularly in vapor lamps, andparticularly the anode stem. The aforesaid Miller patent application isdirected to the use of a heat-confining shield placed around one or bothstems to confine heat ahd reduce the temperature gradient along thestem-seal region, to reduce the likelihood of the seal cracking.

SUMMARY OF THE INVENTION Objects of the invention are to provide animproved lamp and reflector assembly, and to provide such an assemblythat has improved optical efficiency and reduced likelihood of sealcracking.

The invention comprises, briefly and in a preferred embodiment, a lampof the type having a bulb portion and at least one lead-in stemextending therefrom, said lamp being positioned in a concave reflectorhaving a hollow collar extending axially of the reflector at the rearthereof, a lead-in stem of said lamp extending within said hollowcollar, and means attaching said lamp to said reflector at the endregion of said stem within said hollow collar, whereby the hollow collarprovides a heat-confining space around the stem. The hollow collar maybe tapered for further controlling the temperature gradient. In anembodiment of the invention, the lamp is provided with a second lead-instem extending forwardly of the bulb portion, and a lead-in connectorextends into the concave reflector from said hollow collar and is shapedto extend frontwardly within the reflector in adjacency to the innersurface thereof and thence substantially laterally and into attachmentwith the inlead of said second lead-in stem. Further in accordance withthe invention, the lamp may be an arc lamp for d-c operation havinganode and cathode electrodes respectively terminating in inleads at theends of anode and cathode stems extending in opposite directions fromthe bulb portion, it being the anode stem that extends into said hollowcollar and is attached thereto.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a front view of a lamp andreflector assembly in accordance with a preferred embodiment of theinvention, and

FIG. 2 is a cross-sectional view of FIG. 1, taken on the line 2-2thereof, the cross-section of the reflector being taken through an axisthereof, and the lamp and connector leads being shown in side view.

DESCRIPTION OF THE PREFERRED EMBODIMENT The lamp shown in the drawing isa compact high-intensity arc tube lamp 11, comprising a quartz envelopehaving a bulb portion 12 and stem portions 13 and 14 extending therefromon opposite sides thereof, on a common axis. Elongated tungsten anodeand cathode electrodes 16 and 17 are positioned on the axis of the lampwith the inner ends thereof spaced apart within the bulb portion 12, andrespectively extend into the anode stem 13 and the cathode stem 14. Theouter ends of the anode and cathode electrodes 16 and 17 arerespectively welded to molybdenum foils 18 and 19, these foils in turnbeing welded to inleads 21 and 22. In the process of manufacture, thefoils 18 and 19 are wetted by the quartz of the stems l3 and 14, toprovide hennetic seals. The lamp contains an ionizable filling whichincludes an inert gas such as argon and a halogen or metal halide suchas indium iodide. Further details of the lamp l1 and its manufacture aredisclosed in U.S. Pat. No. 3,305,289 of Elmer G. Fridrich, issued Feb.21, 1967 and assigned to the same assignee as the present invention. Thelamp shown is intended for direct-current operation, which causes theanode electrode 16 to operate at a considerably higher temperature thanthe cathode electrode 17, and therefore the anode electrode 16 is madethicker and longer than the cathode electrode 17. A concave reflector 26preferably is made of glass and has an ellipsoidal inner surface coveredwith a reflective coating 27. The inner surface of the reflector may beprovided with radial gores to relatively increase the light intensity atthe outer periphery of the projected light beam. The inner or rear partof the reflector 26 terminates in a hollow collar 28 extendingrearwardly of the concave reflector surface 27, coaxially with theoptical axis 29 of the reflector surface 27. The inner diameter of thehollow collar 28 tapers toward a relatively smaller diameter at the rearthereof.

The are tube lamp 11 is mounted along the optical axis 29, with theanode stem 13 extending into the hollow collar 28, and with the arcregion of the lamp coinciding with the near focus point fl of thereflector surface 27. Preferably, the anode stem 13 and the hollowcollar 28 are dimensioned so that end of the anode stem 13 lies in aplane common with the rear end .of the hollow collar 28, as shown. Theend portion of the anode stem 13 is attached to the end region of thehollow collar 28 he means of a refractory cement 31. In manufacture, thearc tube 11 may be adjusted so that the brightest part of the arcthereof is exactly at the near focus fl of the reflector, and held inthis position until the cement 31 hardens. More cement 31 is addedlater, as will be described, for attaching a ceramic end cap to theassembly. The end of the anode stem 13 may be provided with an outwardlyextending flange 32, if desired, to facilitate secure anchoring of theend region of the anode stem 13 in the cement 31.

A cathode connector conductor 36 is shaped to have an end portion 37thereof extend outwardly of the hollow collar 28, through a slot oropening 38 in the wall of the hollow collar 28. The connector 36 isshaped, as shown, so as to extend frontwardly out of the hollow collar28 and to extend frontwardly within the reflector 26 in adjacency to theinner reflecting surface 27 thereof, and thence substantially laterallyinwardly at 39 and into welded attachment with the cathode inlead 22 ofthe arc tube 11. The connector 36 may be secured to the hollow collar 28at the slot 38 thereof, by means of a glob of the cement 31.

Flexible insulated anode and cathode connector leads 41 and 42 areprovided, an end of the flexible anode lead wire 41 being welded to theanode inlead 21, and an end of the flexible conductor of wire 42 beingwelded to the outwardly extending end of the cathode connector 36. Inmanufacture, after the flexible conductors -41 and 42 have beenconnected as described, additional cement 31 is applied at the rear ofthe anode stem 13 and hollow collar 28, for securing a cup-shapedceramic end cap 43 over and around the hollow collar 28, as shown. Thisadditional cement also fills into a portion of the collar slot 38, thuslocking the mass of cement 31 to the collar 28 and preventing rotationwith respect thereto. A slot or other suitable opening 44 is provided inthe wall of the cover 43, through which the anode and cathode flexibleinsulated connectors 41 and 42 extend externally of the assembly. Theouter ends of the flexible conductors 41 and 42 may be provided with aplug or other means for connecting the wires to a source of electricalpower for operating the lamp 1 1.

Preferably the cathode inlead 22 and the exposed portion of the cathodeconnector 36 are coated with a ceramic glaze or other suitableelectrical insulation, for reducing electrical shock hazard.

in accordance with a feature of the invention, the inside diameter ofthe hollow collar 28 is larger than the outer diameter of the anode stem13, thereby defining a heat-confining space around the anode stem 13 andalong a substantial portion of the length thereof, thus causing a moreuniform and more gradual temperature gradient along the anode stem 13,and particularly at the region of the hermetic sealto the foil 18,thereby reducing the likelihood of cracking of the anode stem,particularly at the hermetic seal region thereof. The inner diameter ofthe hollow collar may be tapered, as shown, to further control thetemperature gradient. Also, in accordance with a feature of theinvention, the cathode connector 36 is shaped as shown, i.e., inadjacency with the inner reflective surface 27 insofar as feasible, andthis arrangement is found to minimize shadow and light obstructioneffects by the cathode connector 36.

The construction of the invention, as described above, increases theefficiency and light output of the assembly, over the crosswise-mountedarc tube arrangement of the aforesaid Taillon patent. Due to the axialmounting of the arc tube with respect to the reflector, a full circle ofradiation from the arc tube illuminates a full circle of the reflectivesurface of the reflector, this cooperative effect improving thecollection efficiency of the system. These factors contribute moretowards increasing the overall light output, than the slight reductionof light output caused by the cathode stem 14 being in front of the arcbulb 12.

While a preferred embodiment of the invention has been shown anddescribed, various other embodiments and modifications thereof willbecome apparent to persons skilled in the art, and will fall within thescope of invention as defined in the following claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A lamp and reflector assembly comprising a lamp having an envelopeincluding a bulb portion and an elongated lead-in stem extending fromthe bulb portion, and a concave reflector provided with a hollow collarcoaxial with the optical axis of said reflector at the rear thereof, andattachment means positioning said lamp with respect to said reflectorsuch that said lead-in stem extends into said hollow collar, said hollowcollar having an inner diameter greater than the outer diameter of saidlead-in stem thereby defining a heatconfining space around and along atleast a portion of said lead-in stem and adapted to control thetemperature along said lead-in stem when said lamp is operating, saidinner diameter of said hollow collar being tapered along the axisthereof.

2. An assembly as claimedin claim 1, in which said inner diameter of thehollow collar tapers toward a relatively smaller diameter at the rearthereof.

3. A lamp and reflector assembly comprising a lamp having an envelopeincluding a bulb portion and a first elongated lead-in stem extendingfrom the bulb portion, and a concave reflector provided with a hollowcollar coaxial with the optical axis of said reflector at the rearthereof, and attachment means positioning said lamp with respect to saidreflector such that said lead-in stem extends into said hollow collar,said hollow collar having an inner diameter greater than the outerdiameter of said lead-in stem thereby defining a heatlead-in stemextending from the bulb portion in the opposite direction from the firstlead-in stem, and a leadin connector positioned to extend from saidhollow collar into said concave reflector, said lead-in connector beingshaped to extend forwardly within the reflector in adjacency to theinner surface thereof and thence substantially laterally and intocontact with the inlead of said second lead-in stem.

4. An assembly as claimed in claim 3, in which said lamp is adirect-current arc lamp having anode and cathode electrodes, said firstlead-in stem providing electrical connection to said anode electrode andsaid second lead-in stem providing electrical connection to said cathodeelectrode.

5. An assembly as claimed in claim 3, in which said hollow collar isprovided with an opening through the wall thereof, and in which an endregion of said lead-in connector is shaped to extend laterally outwardlythrough said opening.

6. An assembly as claimed in claim 5, in which said opening in thecollar wall is at the outer end of the collar, said attachment meanscomprising cement configured to hold the outer end region of said firstlead-in stem with respect to the outer end of said hollow collar, saidcement extending into said opening in the wall of the collar to preventrelative rotation with respect thereto. 4

7. An assembly as claimed in claim 5, including a pair of flexibleconductors electrically connected respectively to said outwardlyextending end region of said lead-in connector and to the inlead of saidfirst lead-in stem.

8. An assembly as claimed in claim 6, including a cap member attached tothe rear of said reflector over said hollow collar, said cap memberbeing provided with an opening in the wall thereof, said pair offlexible conductors extending outwardly through said opening of the capmember.

9. An assembly as claimed in claim 3, in which said inner diameter ofsaid hollow collar is tapered along the axis thereof. v

10. An assembly as claimed in claim 9, in which said inner diameter ofthe hollow collar tapers toward a relatively smaller diameter at therear thereof.

1. A lamp and reflector assembly comprising a lamp having an envelopeincluding a bulb portion and an elongated lead-in stem extending fromthe bulb portion, and a concave reflector provided with a hollow collarcoaxial with the optical axis of said reflector at the rear thereof, andattachment means positioning said lamp with respect to said reflectorsuch that said lead-in stem extends into said hollow collar, said hollowcollar having an inner diameter greater than the outer diameter of saidlead-in stem thereby defining a heat-confining space around and along atleast a portion of said lead-in stem and adapted to control thetemperature along said lead-in stem when said lamp is operating, saidinner diameter of said hollow collar being tapered along the axisthereof.
 2. An assembly as claimed in claim 1, in which said innerdiameter of the hollow collar tapers toward a relatively smallerdiameter at the rear thereof.
 3. A lamp and reflector assemblycomprising a lamp having an envelope including a bulb portion and afirst elongated lead-in stem extending from the bulb portion, and aconcave reflector provided with a hollow collar coaxial with the opticalaxis of said reflector at the rear thereof, and attachment meanspositioning said lamp with respect to said reflector such that saidlead-in stem extends into said hollow collar, said hollow collar havingan inner diameter greater than the outer diameter of said lead-in stemthereby defining a heat-confining space around and along at least aportion of said lead-in stem and adapted to control the temperaturealong said lead-in stem when said lamp is operating, said lamp envelopeincluding a second elongated lead-in stem extending from the bulbportion in the opposite direction from the first lead-in stem, and alead-in connector positioned to extend from said hollow collar into saidconcave reflector, said lead-in connector being shaped to extendforwardly within the reflector in adjacency to the inner surface thereofand thence substantially laterally and into contact with the inlead ofsaid second lead-in stem.
 4. An assembly as claimed in claim 3, in whichsaid lamp is a direct-current arc lamp having anode and cathodeelectrodes, said first lead-in stem providing electrical connection tosaid anode electrode and said second lead-in stem providing electricalconnection to said cathode electrode.
 5. An assembly as claimed in claim3, in which said hollow collar is provided with an opening through thewall thereof, and in which an end region of said lead-in connector isshaped to extend laterally outwardly through said opening.
 6. Anassembly as claimed in claim 5, in which said opening in the collar wallis at the outer end of the collar, said attachment means comprisingcement configured to hold the outer end region of said first lead-instem with respect to the outer end of said hollow collar, said cementextending into said opening in the wall of the collar to preventrelative rotation with respect thereto.
 7. An assembly as claimed inclaim 5, including a pair of flexible conductors electrically connectedrespectively to said outwardly extending end region of said lead-inconnector and to the inlead of said First lead-in stem.
 8. An assemblyas claimed in claim 6, including a cap member attached to the rear ofsaid reflector over said hollow collar, said cap member being providedwith an opening in the wall thereof, said pair of flexible conductorsextending outwardly through said opening of the cap member.
 9. Anassembly as claimed in claim 3, in which said inner diameter of saidhollow collar is tapered along the axis thereof.
 10. An assembly asclaimed in claim 9, in which said inner diameter of the hollow collartapers toward a relatively smaller diameter at the rear thereof.